Electrodeposited Cu–ZnO and Mn–Cu–ZnO nanowire/tube catalysts for higher alcohols from syngas

Cu–ZnO and Mn–Cu–ZnO catalysts have been prepared by electrodeposition and tested for the synthesis of higher alcohols via CO hydrogenation. The catalysts were prepared in the form of nanowires and nanotubes using a nanoporous polycarbonate membrane, which served as a template for the electrodeposition of the precursor metals from an aqueous electrolyte solution. Electrodeposition was carried out using variable amounts of Zn(NO₃)₂, Cu(NO₃)₂, Mn(NO₃)₂ and NH₄NO₃ at different galvanostatic conditions. A fixed bed reactor was used to study the reaction of CO and H₂ to produce alcohols at 270 °C, 10–20 bar, H₂/CO = 2/1, and 10,000–33,000 scc/h g_cat. In addition to methane and CO₂, methanol was the main alcohol product. The addition of manganese to the Cu–ZnO catalyst increased the selectivity toward higher alcohols by reducing methane formation; however, CO₂ selectivity remained high. Maximum ethanol selectivity was 5.5%, measured as carbon efficiency.     

Adsorption of Heavy Metals from Aqueous Solutions onto Activated Carbon in Single Cu and Ni Systems and in Binary Cu–Ni,Cu–Cd and Cu–Zn Systems

Single copper and nickel adsorption from aqueous solutions onto a granular activated carbon is reported. Metal removals increase on raising pH and temperature, and decrease on raising the initial metal concentration at constant carbon dose. The adsorption processes are modelled using the surface complex formation (SCF) Triple Layer Model (TLM) with an overall surface bidentate species. A dependence of the SCF constant on pH, initial molar metal/carbon ratio and temperature is observed, and a correlation for log K_ads is determined. The SCF model successfully predicts copper and nickel removals in single metal solutions. Adsorption in the binary metal systems copper–nickel, copper–cadmium and copper–zinc is also reported, showing competitive adsorption effects. © 1997 SCI.     

Epoxidation of styrene over mesoporous Zr–Mn-MCM-41

Epoxidation of styrene with t-butyl hydroperoxide (TBHP) as an oxidizing agent has been conducted under liquid phase reaction conditions over Zr–Mn-MCM-41 with different n_Si/(n_Zr + n_Mn) ratios and Mn-MCM-41(31) catalysts for selective synthesis of styrene oxide. The influences of various reaction parameters such as temperature, time, oxidants, and solvents, styrene to TBHP mmol ratios and acetonitrile (MeCN) to N,N-dimethylformamide (DMF) volume ratios on the conversion of styrene and the selectivity of styrene oxide have also been studied. With the decrease of the n_Si/(n_Zr + n_Mn) ratios of Zr–Mn-MCM-41 catalysts from 327 to 49, the conversion of styrene as well as the yield and selectivity of styrene oxide increase due to the increase of the number of Lewis acid sites on the surface of catalysts. Moreover, the conversion and selectivity in Zr–Mn-MCM-41(49) is higher as compared to that of Mn-MCM-41(31). The Zr–Mn-MCM-41(49) is found to be reusable for the epoxidation of styrene with TBHP for selective synthesis of styrene oxide.     

Structure, thermal-stability and reducibility of Si-doped Ce–Zr–O solid solution

The Si-doped Ce–Zr–O solid solutions have been prepared by the reverse microemulsion method. The effects of Si and its content on the structure characters, thermal-stability and reducibility of the Ce–Zr–O solid solution have been studied by N₂ adsorption, XRD, laser Raman (LR), TPR, FT-IR, NMR and XPS methods. The results indicate that, there are the bonds of Si–O–M (Ce or Zr) in the Ce–Zr–Si–O solid solutions, and the presence of Si can increase obviously the surface area, thermal-stability, crystal lattice distortion rate, and reducibility of the solid solution. The surface area of the sample with 20 wt.% Si reaches 153 m² g⁻¹ after being calcined at 900 °C for 6 h. The Ce–Zr–O solid solution with 5.2–10 wt.% Si shows excellent thermal-stability and reducibility.     

Intermetallic powders of Ni–Al, Cu–Al and Cr–Al systems obtained by the self-disintegration method

The intermetallic compounds of the Ni–Al, Cu–Al and Cr–Al systems are characterised by the profitable set of mechanical and physical properties, such as good abrasion resistance, high temperature oxidation and sulfur corrosion resistance.

Alloy powders, among them intermetallic powders, are widely used and methods of their production are under development. The technology described here takes advantage of a natural phenomenon, i.e. self-disintegration which takes place in alloys containing Al₄C₃ carbide, e.g. in high aluminium cast iron. The result of chemical reaction between this carbide and moisture are products of bigger volume. It causes cracking of the matrix, i.e. self-disintegration into a powder. The physical–chemical principles of the powder production using self-disintegration are presented in this article.

In Ni–Al–C, Cu–Al–C and Cr–Al–C alloys, Al₄C₃ phase is not present in the liquid melt. Therefore, the presence of a catalysing component, increasing the chemical activity of carbon, is required. Iron can be one of such additions. The mechanism of the influence of the iron on the Al₄C₃ carbide crystallisation and the physical–chemical properties of the powders obtained by the self-disintegration process is presented in this work. Applications (plasma spraying, powder metallurgy) of the intermetallic powders obtained in this way are mentioned.     

Thermal and chemical stability of Cu–Zn–Cr-LDHs prepared by accelerated carbonation

Layered double hydroxides Cu_xZn_6 − xCr₂(OH)₁₆(CO₃)·4H₂O with different molar ratios of Cu/Zn/Cr were synthesized by accelerated carbonation. The products were characterized by XRD, SEM, FT-IR and TG-DTG-DSC-MS. The chemical stability was tested by the modified Toxicity Characteristic Leaching Procedure (TCLP). The results showed that the products were the mixture of Cu_xZn_6 − xCr₂(OH)₁₆(CO₃)·4H₂O and (CuZn)₂(CO₃)(OH)₂, with similar thermal behavior. All products were chemically stable with reduced leaching at pH > 6 (Cu²⁺, Zn²⁺) or > 5 (Cr³⁺).     

Elastic,mechanical, electronic,and defective properties of Zr–Al–C nanolaminates from first principles

By means of first principles calculations, Zr–Al–C nanolaminates have been studied in the aspects of chemical bonding, elastic properties, mechanical properties, electronic structures, and vacancy stabilities. Although the investigated Zr–Al–C nanolaminates show crystallographic similarities, their predicated properties are very different. For (ZrC)_nAl₃C₂ (n = 2, 3, 4), the Zr–C bond adjacent to the Al–C slab with the C atom intercalated in the Zr layers is the strongest, but the one with the C atom intercalated between the Zr layer and Al layer is the weakest. In contrast, the situation for (ZrC)_nAl₄C₃ (n = 2, 3) is just the opposite. For Zr–Al–C nanolaminates, the calculated bulk, shear and Young's modulus increase in the sequence of Zr₂AlC < Zr₃AlC₂ < Zr₂Al₄C₅ < Zr₃Al₄C₆ < Zr₂Al₃C₄ < Zr₃Al₃C₅ < Zr₄Al₃C₆. The (ZrC)_nAl₃C₂ (n = 2, 3, 4) series exhibit the most outstanding elastic properties. In the presence of the external pressure, the bulk and shear moduli exhibit a linear response to the pressure, except for Zr₂AlC and Zr₃AlC₂, both of which belong to the so‐called MAX phases. The two materials also exhibit very distinct properties in the strain‐stress relationship, electronic structures and vacancy stabilities. As the intercalated Al layers increase, the formation energy of V_Zr and V_Al increases, while the formation energy of V_C decreases.     

Thermal behaviour of Cu–Mg–Mn and Ni–Mg–Mn layered double hydroxides and characterization of formed oxides

Thermal behaviour of synthetic Cu–Mg–Mn and Ni–Mg–Mn layered double hydroxides (LDHs) with M^II/Mg/Mn molar ratio of 1:1:1 was studied in the temperature range 200–1100 °C by thermal analysis (TG/DTA/EGA), powder X-ray diffraction (XRD), Raman spectroscopy, and voltammetry of microparticles. Powder XRD patterns of prepared LDHs showed characteristic hydrotalcite-like phases, but further phases were indirectly found as admixtures. The Cu–Mg–Mn precipitate was decomposed at temperatures up to ca. 200 °C to form an XRD-amorphous mixture of oxides. The crystallization of CuO (tenorite) and a spinel type mixed oxide of varying composition Cu_xMg_yMn_zO₄ with Mn⁴⁺ was detected at 300–500 °C. At high temperatures (900–1000 °C), tenorite disappeared and a consecutive crystallization of 2CuO·MgO (gueggonite) was observed. The high-temperature transformation of oxide phases led to a formation of Cu^I oxides accompanied by oxygen evolution. The DTA curve of Ni–Mg–Mn sample exhibited two endothermic effects characteristic for hydrotalcite-like compounds. The first one with minimum at 190 °C can be ascribed to a loss of interlayer water, the second one with minimum at 305 °C to the sample decomposition. Heating of the Ni–Mg–Mn sample at 300 °C led to the onset of crystallization of oxide phases identified as Ni_xMg_yMn_zO₄ spinel, (Ni,Mg)O oxide containing Mn⁴⁺ cations, and easily reducible XRD-amorphous species, probably free Mn^III,IV oxides. At 600 °C (Raman spectroscopy) and 700 °C (XRD), the (Ni,Mg)₆MnO₈ oxide with murdochite structure together with spinel phase were detected. Only spinel and (Ni,Mg)O were found after heating at 900 °C and higher temperatures. Temperature-programmed reduction (TPR) profiles of calcined Cu–Mg–Mn samples exhibited a single reduction peak with maximum around 250 °C. The highest H₂ consumption was observed for the sample calcined at 800 °C. The reduction of Ni–Mg–Mn samples proceeded by a more complex way and the TPR profiles reflected the phase composition changing depending on the calcination temperature.     

Catalytic combustion of toluene over mixed Cu–Mn oxides

The influence of the synthesis pH and of the Zn and/or Al additives on the Cu–Mn precursors, obtained by co-precipitation at a constant pH from aqueous solutions of appropriate nitrates at (Cu + Zn)/(Mn + Al) ratio equal 2, was investigated. The relative content of Mn increased with the pH of precipitation. Depending on the sample composition the identified crystalline phases included layered hydroxy double salt, hydrotalcite-like structure, CuO and ZnO. Some precursors had strongly amorphous character. Calcination of the precursors at 673 K resulted in mixed oxides, in which CuO of various degrees of crystallinity could be identified. The Mn-containing phases remained amorphous. All calcined materials proved extremely active in catalytic combustion of toluene. Some catalysts reached 100% conversion already at 403 K. High conversions observed in the low temperature regime were partially due to the strong sorption of toluene. In the catalysts containing Al additive this effect was suppressed.     

Selective hydroxylation of phenol employing Cu–MCM-41 catalysts

We studied the oxidation reaction of phenol in aqueous and acetonitrile media under mild conditions, employing Cu-modified MCM-41 mesoporous catalysts. The stability of the catalysts under reaction conditions was confirmed by XRD, UV–VIS and FTIR techniques. Results obtained indicate that the selective oxidation of phenol with H₂O₂ by a radical substitution mechanism produces three main reaction products: catechol, hydroqinone and benzoquinone.     

Joining of sintered silicon carbide using ternary Ag–Cu–Ti active brazing alloy

Sintered silicon carbide was brazed to itself by Ag–35.25 wt%Cu–1.75 wt%Ti filler alloy at 860 °C, 900 °C and 940 °C for 10 min, 30 min and 60 min. Mechanical properties both at room temperature and high temperature were measured by flexural strength. The interfacial microstructure was investigated by electron probe microanalysis (EPMA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The experimental results indicate that increased brazing temperature heightens the flexural strength and the maximal four-point flexural strength reaches 342 MPa at room temperature. In addition longer holding times result in thicker reaction layer, which increases mismatch of coefficients of thermal expansion (CTE) between SiC substrate and reaction layer and finally leads to poor mechanical properties due to high residual stresses. High temperature flexural strength decreases with an increase of test temperature due to softening of the filler alloy. A reaction layer composed of TiC and Ti₅Si₃ was observed at the interface of SiC/filler alloy and there is a representative microstructure: SiC/continuous fine TiC layer/discontinuous coarse Ti₅Si₃ layer/filler alloy.     

Methanol reforming for fuel-cell applications: development of zirconia-containing Cu–Zn–Al catalysts

The steam reforming of methanol to form mixtures of carbon dioxide and hydrogen, together with traces of carbon monoxide, is considered to be a potential source of hydrogen as the fuel for a fuel-cell to be used in mobile power sources. After outlining some of the constraints inherent in the use of the reaction and the types of catalysts which have been used by other investigators, this paper presents results on the preparation and testing of a series of copper-containing catalysts for this reaction. It is shown that the reaction sequence probably involves the formation of methyl formate which then decomposes to give CO₂ as the primary product; CO is formed by the reverse water–gas shift reaction and this only occurs to an appreciable extent when the methanol is almost completely converted. A number of different copper-containing catalysts are then described and it is shown that of these sequentially precipitated Cu/ZnO/ZrO₂/Al₂O₃ materials have the highest activities and stabilities for the steam reforming reaction.     

A novel catalyst fabricated from Al–Cu–Fe quasicrystal for steam reforming of methanol

The optimum preparation condition of Al–Cu–Fe quasicrystalline (QC) catalyst with excellent catalytic performance for steam reforming of methanol (SRM) has been investigated. The QC alloy is superior to the other crystalline Al–Cu–(Fe) alloys (i.e., beta and theta phase) as a catalyst material because of the brittle nature of QC. The wet milling process (in ethanol) for the QC powders is much better than the dry milling process to obtain fine particles with high surface area. The QC powder prepared by the wet process followed by leaching in Na₂CO₃ aq. at 323 K exhibited the highest catalytic performance (activity and stability) in the present study. From these findings, it is clear that the QC catalyst with the excellent catalytic performance could be obtained by controlling the initial grain size of the QC powder and the leaching temperature.     

Relating catalyst structure and composition to the water–gas shift activity of Cu–Zn-based mixed-oxide catalysts

In order to investigate the effect of cerium oxide on Cu–Zn-based mixed-oxide catalysts four catalyst samples were characterized by means of XRD, in situ XANES and thermogravimetric analysis. The activity of the catalyst samples was tested for the forward water–gas shift reaction. Cerium oxide was found to increase the crystallinity of the ZnO phase indicating a segregation of the Cu and ZnO phases. The TOF of the water–gas shift reaction based on chemisorption data was found to be independent of composition and preparation conditions of the four catalyst samples. In contrast, the catalyst stability depends on composition and preparation conditions. Cerium oxide impregnated before calcination of the hydrotalcite-based Cu–Zn precursors leads to a more stable water–gas shift catalyst.     

A Coated Infiltration Growth Technique for Fabricating Single‐Grain Y–Ba–Cu–O Bulk Superconductor

A coated infiltration growth technique was proposed to fabricate single‐grain Y?Ba?Cu?O bulk superconductor, in which a liquid source coated Y₂BaCuO₅ (Y‐211) preform was employed and the liquid source composition was 3BaO + 5CuO. Experimental results indicated that, the sample exhibited a single‐grain morphology on the top surface, and the liquid source coating always existed surrounding the bulk which contributed to the complete growth of the sample. The homogeneous distribution of fine Y‐211 inclusions in microstructure and a satisfactory J_c performance of 5.67 × 10⁴ A/cm² in self‐field at 77 K have also been observed.     

Influence of Ca/Al Ratio on Properties of Amorphous/Nanocrystalline Cu–Al–Ca–O Thin Films

This article reports the characterization of thin films sputtered from CuAl_1?xCa_xO targets (x = 0, 0.05, 0.1, 0.15, and 0.2) at room temperature. All films exhibit amorphous/nanocrystalline structures. Their transparency increases slightly with the addition of Ca. Furthermore, the resistivity decreases as the Ca/Al atomic ratio increases. Transmission electron microscopy with energy dispersive spectroscopy mapping indicates that the composition is uniform throughout the films deposited from the highest Ca doping concentration target. Some nanocrystals are present at the top surface of the CuAl_0.8Ca_0.2O thin film as well as the interface region between the CuAl_0.8Ca_0.2O thin film and the glass substrate, whereas the interior of the film is pretty amorphous with some embedded nanocrystals. X‐ray photoelectron spectroscopy shows that the Cu²⁺/Cu⁺ atomic ratio increases with the Ca/Al atomic ratio, indicating the enhancement of p‐type conductivity from the nonisovalent Cu–O alloying.     

Reaction Pathway of Combustion Synthesis of Ti5Si3 in Cu–Ti–Si System

The reaction pathway of combustion synthesis (CS) of Ti₅Si₃ in Cu–Ti–Si system was explored through a delicate microstructure and phase analysis on the resultant products during differential thermal analysis (DTA). The formation of Cu–Si eutectic liquids plays a key role in the reaction pathway, which provides easy route for reactant transfer and accelerates the occurrence of complete reaction. Cu initially reacted with Si to form Cu₃Si by a solid‐state diffusion reaction, which further reacted with Cu to form Cu–Si liquids at the eutectic point of ~802°C; then Ti was dissolved into the surrounding Cu–Si liquids and led to the formation of Cu–Ti–Si ternary liquids; finally, Ti₅Si₃ was precipitated out of the saturated liquids by a solution–reaction–precipitation mechanism. The reaction pathway in CS of titanium silicide (Ti₅Si₃) could be described briefly as: Cu_(s) + Ti_(s) + Si_(s)→Cu₃Si_(s) + Ti_(s) + Si_(s)→(Cu–Si)_(l) + Ti_(s)→(Cu–Ti–Si)_(l)→Cu_(l) + Ti₅Si_3(s).     

A Cu–Pd–V System Filler Alloy for Silicon Nitride Ceramic Joining and the Interfacial Reactions

A Cu–Pd–V brazing alloy with the composition of Cu–(38.0~42.0)Pd–(7.0~10.0)V (in wt.%) was designed as a filler for joining Si₃N₄. Its wettability on Si₃N₄ ceramic was measured with the sessile drop method. It was shown that the Cu–Pd–V alloy gave a contact angle of 71° at 1473 K. The filler alloy was fabricated into foils with a thickness of 0.15 mm. The Si₃N₄–Si₃N₄ joints brazed at 1443 K for 10 min exhibit average three‐point bend strength of 263 MPa at room temperature, and the joint strengths at 973 K and 1073 K are 277 MPa and 218 MPa, respectively. The analysis results of SEM, XRD, and TEM for the brazed joint indicate the presence of V₂N at the surface of the Si₃N₄. The increase of the thickness of V₂N reaction layer obeyed parabolic law, and the parabolic rate constant (k) can be described as k = 2.8739 × 10^?9 exp(?162989.4/RT) m²/s. Pd₂Si and Cu₃Pd compounds as well as (Cu, Pd) solid solution were detected in the central part of the joints. The presence of (Cu, Pd) phases and especially refractory Pd₂Si compounds within the joints should contribute to the stable high‐temperature property. The interfacial reaction mechanisms were discussed.     

Syntheses of Spinon Thermal Conductivity Materials in Sr–Cu–O System by Glass‐Ceramics Technique

We have synthesized spinon thermal conductivity materials in Sr–Cu–O system by glass‐ceramics technique. The materials are promising for active control of thermal energy in microelectronic devices because of high and anisotropic thermal conduction, its controllability, and electric insulation. Nevertheless, research on these materials has been limited to that concerning theoretical perspectives and investigation of physical properties using large single crystals. In this study, we adopt glass‐ceramics technique to synthesize these materials: We prepared melt‐quenched multicomponent oxides including SrO and CuO, and checked its glass‐forming ability and crystallization behaviors by heating. As a result, we have found that SrCuO₂ and Sr₁₄Cu₂₄O₄₁, known as the spinon thermal conductivity materials, are synthesized using SrO–CuO–?Li₂O–?Al₂O₃?–Ga₂O₃ system. This synthesis process for the system will provide practical application of the spinon thermal conductivity materials.